A vitrified superabrasive grain grinding stone, because of bonding of superabrasive grains by melting down an inorganic vitrified bond at calcination temperature in the order of, for example, 500 to 1000° C., can have a high abrasive grain holding power, namely, a high adhesive power between the superabrasive grains and the vitrified bond, as compared with the case of using an organic resin bond. For example, in the case of CBN abrasive grain, it is considered that, since B element, and K or Na element, etc., within a catalyst, added during a synthesis process thereof, are present on a surface thereof, these elements react with the vitrified bond and their chemical bonding power heightens the abrasive grain holding power.
Conventionally, out of steel-made work materials, a shaft component such as a camshaft and a crankshaft as a main component of an automobile engine is subjected to a high-precision grinding process for enhancement of performance of the engine but there have been problems of processing deformation, lowered hardness, and residual stress caused to the shaft component as the work material by a grinding heat generated at the time of grinding. As to a general countermeasure to eliminate the occurrence of these problems, proposals are made such as (a) using a clean-cutting grinding stone, (b) reducing an amount of cutting at grinding time, using a porous grinding stone, (c) lessening processing conditions by using a soft grinding stone of a low binding degree, (d) cooling by a sufficient supply of a coolant to a grinding point, and (e) using a grind stone with the CBN abrasive grain and a diamond abrasive grain mixed at various ratios. Such grinding stones are those described, for example, in Patent Document 1, Patent Document 2, and Patent Document 3.